JP5052363B2 - Liquid crystal element - Google Patents

Description

  The present invention relates to a liquid crystal element using a liquid crystal as an electro-optic effect, and particularly to a liquid crystal element using a smectic liquid crystal as the liquid crystal.

  Ferroelectric liquid crystals and antiferroelectric liquid crystals are generally known as liquid crystals exhibiting a smectic phase. Both liquid crystals have spontaneous polarization and are used as a display for display by changing the direction of spontaneous polarization under the influence of an external electric field or magnetic field. A liquid crystal electro-optical element using a ferroelectric liquid crystal has been reported by Clark et al. To have a memory property and a high-speed response.

  A ferroelectric liquid crystal has a plurality of optical states and has a characteristic of maintaining a specific state without applying a voltage. The ferroelectric liquid crystal molecules take one of two stable positions along the side of the cone (liquid crystal cone) according to the external influence such as an electric field. When a ferroelectric liquid crystal is sandwiched between a pair of substrates and used as a liquid crystal display device, the ferroelectric liquid crystal molecules are in any of the two stable positions described above according to the polarity of the voltage applied to the ferroelectric liquid crystal. Control to be located on either side. One of the two stable positions is called the first ferroelectric state, and the other is called the second ferroelectric state.

  FIG. 1 shows a configuration example of a liquid crystal panel 20 using a ferroelectric liquid crystal 10. In FIG. 1, polarizing plates 15a (the direction of the polarization axis is a) and 15b (the direction of the polarization axis is b) are arranged in crossed Nicols. Further, the long axis direction of the molecules of the ferroelectric liquid crystal 10 in the second ferroelectric state is arranged so as to coincide with the polarization axis a. Therefore, the major axis direction of the liquid crystal molecules in the first ferroelectric state is another position along the liquid crystal cone as shown in FIG.

  As shown in FIG. 1, when the polarizing plates 15a and 15b and the ferroelectric liquid crystal 10 are arranged and the polarity of the applied voltage is changed to bring the ferroelectric liquid crystal 10 into the second ferroelectric state (ferroelectric property). When the major axis direction of the molecules of the liquid crystal 10 coincides with the polarization axis a of the polarizing plate 15a), no light is transmitted, and the liquid crystal panel 20 is displayed in black (non-transmissive state). Further, when the polarity of the applied voltage is changed to place the ferroelectric liquid crystal 10 in the first ferroelectric state (the major axis direction of the molecules of the ferroelectric liquid crystal 10 is the polarization axis a of the polarizing plate 15a and the polarizing plate 51b), the major axis direction of the liquid crystal molecules is inclined at a certain angle with respect to the polarization axis, so that, for example, light from the backlight is transmitted, and the liquid crystal panel 20 displays white ( Transmission state). Note that a light source other than the backlight can be used for display.

  Next, switching of the ferroelectric liquid crystal 10, that is, transition from one ferroelectric state to the other ferroelectric state will be described with reference to FIG. As shown in FIG. 2, the voltage applied to the ferroelectric liquid crystal 10 is increased, the voltage value at which the light transmittance starts to increase is V1, the voltage is further increased, and the voltage value at which the increase in the light transmittance is saturated. Let V2 be a positive threshold. Conversely, the voltage applied to the ferroelectric liquid crystal 10 is decreased, the voltage value at which the light transmittance starts to decrease is V3, the voltage is further decreased, and the voltage value at which the decrease in light transmittance is saturated is V4 (negative Threshold). Here, the state where the light transmittance is high is the first ferroelectric state, and the state where the light transmittance is low is the second ferroelectric state.

  For example, when a voltage value equal to or higher than V2 is applied to the ferroelectric liquid crystal 10, the ferroelectric liquid crystal transitions to the first ferroelectric state, and thereafter, even if no voltage is applied (that is, 0 V is applied), the ferroelectric liquid crystal The liquid crystal retains the first dielectric state. Similarly, when a voltage value equal to or lower than V4 is applied to the ferroelectric liquid crystal, the ferroelectric liquid crystal transitions to the second ferroelectric state, and after that, even if no voltage is applied (that is, 0 V is applied), the ferroelectric liquid crystal is changed. The liquid crystal retains the second dielectric state. As described above, after the ferroelectric liquid crystal is applied with a voltage equal to or higher than the positive threshold value or lower than the negative threshold value and transitions to a predetermined ferroelectric state, the state remains as it is without applying a voltage. Will be held. Such a ferroelectric liquid crystal is described in Patent Document 1, for example.

  A liquid crystal panel using a ferroelectric liquid crystal is sandwiched between a pair of substrates provided with an alignment film and aligned in a bookshelf type or chevron type layer structure. By applying a pulse electric field to the liquid crystal, liquid crystal molecules can be driven in parallel with the substrate surface. In addition, when a ferroelectric liquid crystal is used and a display element having a memory property is formed, an SiO alignment film is used.

  FIG. 3 is a configuration diagram of the liquid crystal cell 22 showing the arrangement of polarizing plates when an antiferroelectric liquid crystal is used as a display. Between the polarizing plates 21a and 21b matched to crossed Nicols, the liquid crystal cell 22 is placed so that the polarization axis of one of the polarizing plates and the major axis direction of the average molecule when no voltage is applied are substantially parallel. Black is displayed when no voltage is applied, and white is displayed when an electric field is applied.

  FIG. 4 is a diagram showing the relationship between the transmittance of the liquid crystal cell 22 using antiferroelectric liquid crystal and the applied voltage. When the voltage is applied and increased, the voltage value at which the transmittance starts to change is V11, the voltage value at which the transmittance change is saturated is V12, and conversely, when the voltage value is decreased, the transmittance starts to decrease. When the voltage value is V15 and a voltage of reverse polarity is applied and the absolute value is increased, the voltage value at which the transmittance starts to change is V13, the voltage value at which the transmittance change is saturated is V14, and the absolute voltage A voltage value at which the transmittance starts to change when the value is decreased is defined as V16.

  As shown in FIG. 4, the first ferroelectric state is selected when the voltage value is greater than or equal to the threshold value of the antiferroelectric liquid crystal molecules. Further, the second ferroelectric state is selected depending on the difference in polarity of the applied voltage. Thus, it can be seen that in the antiferroelectric liquid crystal, the antiferroelectric state is selected from the ferroelectric state when the voltage value is lower than a certain threshold value. Such an antiferroelectric liquid crystal is described in Patent Document 2, for example.

  FIG. 5 is a diagram showing a region in which alignment in a liquid crystal element using a ferroelectric liquid crystal and a SiO alignment film is likely to be unstable. In FIG. 5, the ferroelectric liquid crystal injected from the injection hole 3 is sealed between the two glass substrates 1 and the sealing material 2. Here, the region 6 indicates a region in which the orientation tends to become unstable.

  A smectic liquid crystal such as a ferroelectric liquid crystal is a mixture in which a plurality of compositions are mixed at a predetermined ratio, and has a high viscosity. On the other hand, SiO, which is an alignment film, is porous, and its surface is active especially when it is formed by vapor deposition. In this state, when smectic liquid crystal is injected from the injection hole, when a chromatographic phenomenon occurs between the liquid crystal and the alignment film, the composition of the liquid crystal is adsorbed to the alignment film, and as the liquid crystal is injected, Its composition changes gradually. Therefore, the composition of the liquid crystal is different near the injection hole 3 and at a position far from the injection hole, and at a position far from the injection hole, the alignment state of the liquid crystal tends to be unstable and display unevenness is likely to occur.

  In Patent Document 3, in order to eliminate display unevenness due to concentration unevenness of a liquid crystal material and to obtain uniform display quality, a scanning electrode is arranged in parallel to the liquid crystal injection direction, and a scanning signal is sent to an end opposite to the injection hole. A liquid crystal display element to be added is described. Patent Document 3 describes that a high-polarity component in a liquid crystal material is adsorbed to an alignment film when liquid crystal is injected, and a concentration distribution of the liquid crystal material is generated depending on the position from the injection hole. When a concentration distribution is generated in the liquid crystal material, a driving voltage distribution is generated in the liquid crystal display element. The driving voltage is low near the injection hole and the driving voltage is high on the back side. In addition, a voltage drop occurs due to the sheet resistance of the scan electrode, and the applied voltage changes depending on the position of the electrode. In view of this, the liquid crystal display device described in Patent Document 3 employs a configuration in which scanning electrodes are arranged in parallel with the liquid crystal injection direction and a scanning signal is applied from an end opposite to the injection hole. It is described that such a configuration compensates for the drive voltage distribution caused by the concentration distribution of the liquid crystal material and the voltage drop of the scan electrode, and can apply an appropriate scan voltage and obtain uniform display quality. ing.

JP-A-2006-23481 (FIGS. 1 and 2) JP-A-10-239664 (FIGS. 2 and 3) Japanese Patent Laid-Open No. 4-355433 (page 3, FIG. 2)

  In particular, in the case of a smectic liquid crystal, in a region where the alignment state of the liquid crystal tends to be unstable, a pulse having a voltage lower than the threshold voltage is repeatedly applied, so that the homogeneous alignment easily shifts to the twist alignment, resulting in uneven display. It became clear that it became.

  FIG. 6 is a diagram showing voltages applied to respective pixels when a display element having a memory property using ferroelectric liquid crystal is driven by simple matrix driving in which a plurality of scanning electrodes and signal electrodes are formed in a strip shape. It is. 6A shows driving pulses applied to the first, second, and nth scanning electrodes, and FIG. 6B shows driving pulses applied to the signal electrodes. FIG. 7 shows drive voltages applied to the pixels in each scan electrode. FIG. 7 shows a selection period 7 in which a selection pulse is applied and a non-selection period 8 in which a non-selection pulse is applied.

  In a display element having a memory property, the screen display once written is maintained as it is without disappearing. In addition, in order to rewrite a still screen, it is necessary to scan all the scanning electrodes only once and rewrite the screen. Therefore, a display element having a memory property has a writing period in which all the scanning electrodes are scanned and a screen display holding period in which no voltage is applied. In order to perform an arbitrary screen display, it is only necessary to apply a voltage during the writing period, and it is not necessary to apply a voltage at all during the holding period for maintaining the screen display.

  In the writing period, a scan pulse of ± 2/3 V is applied to the scan electrodes in order from the first one, and a signal pulse of ± 1/3 V corresponding to white or black is applied to the signal electrode. Further, the driving voltage applied to each pixel is the sum of the scanning electrode and the signal electrode.

  As shown in FIG. 7, in the selection period 7, a voltage ± V larger than the threshold for driving the liquid crystal is applied, and white or black is displayed. A voltage ± 1/3 V smaller than the threshold is applied to the non-selection pulse. In the pixel (1, m) on the first scanning electrode, after the selection pulse is applied, the non-selection pulse in the non-selection period 8 is repeatedly applied while the number of remaining scanning electrodes is scanned. Will be. On the other hand, after the non-selection pulse is repeatedly applied to the pixel (n, m) on the n-th scan electrode that is scanned last, the selection pulse is applied last.

  FIG. 8 shows a ferroelectric liquid crystal element in which the scanning electrode 4 is arranged in parallel with the direction in which the liquid crystal is injected, that is, the scanning electrode is arranged in parallel with the direction in which the liquid crystal is injected. A plurality of signal electrodes 5 are arranged perpendicular to the scanning electrodes 4. At this time, the scanning electrodes 4 are scanned in order from the top to the bottom in the drawing along the direction of the arrow. In the pixel 9 (1, m) on the scanning electrode 4 in the first scanning order, as shown in FIG. 7, a selection pulse is first applied, and white or black is displayed. Thereafter, a voltage ± 1/3 V as a non-selection pulse is repeatedly applied by the number of remaining scanning lines. In the position where the scanning order is early, for example, on the first scanning electrode and the pixel overlapping the region 6 where the orientation is likely to be unstable, even if white or black is displayed by the selection pulse, it is not selected after the selection pulse. When a large number of pulses are repeatedly applied, twist alignment occurs and white or black display changes, which may cause display unevenness.

  FIG. 9 shows another ferroelectric liquid crystal element in which the scanning electrode 4 is arranged in parallel with the direction in which the liquid crystal is injected, that is, the scanning electrode is arranged in parallel with the liquid crystal injection direction. The only difference between FIG. 9 and FIG. 8 is that the scanning electrode 4 is scanned in order from the bottom to the top in the figure along the direction of the arrow. Also at this time, as shown in FIG. 7, the selection pulse is first applied to the pixel 9 ′ (1, m) on the scanning electrode 4 in the first scanning order, and white or black is displayed. Thereafter, a voltage ± 1/3 V as a non-selection pulse is repeatedly applied by the number of remaining scanning lines. In the position where the scanning order is early, for example, on the first scanning electrode and the pixel overlapping the region 6 where the orientation is likely to be unstable, even if white or black is displayed by the selection pulse, it is not selected after the selection pulse. When a large number of pulses are repeatedly applied, twist alignment occurs and white or black display changes, which may cause display unevenness.

  FIG. 10 shows still another ferroelectric liquid crystal element in which the scan electrode 4 is arranged perpendicular to the direction in which the liquid crystal is injected, that is, the scan electrode is arranged perpendicular to the liquid crystal injection direction. The difference between FIG. 10 and FIG. 8 is that the arrangement direction of the scanning electrode 4 and the signal electrode 5 is opposite, and that the scanning electrode 4 moves from right to left in the figure along the direction of the arrow. Only points that are scanned in order. Also at this time, as shown in FIG. 7, the selection pulse is first applied to the pixel 9 (1, m) on the scanning electrode 4 in the first scanning order, and white or black is displayed. Thereafter, a voltage ± 1/3 V as a non-selection pulse is repeatedly applied by the number of remaining scanning lines. In the position where the scanning order is early, for example, on the first scanning electrode and the pixel overlapping the region 6 where the orientation is likely to be unstable, even if white or black is displayed by the selection pulse, it is not selected after the selection pulse. When a large number of pulses are repeatedly applied, twist alignment occurs and white or black display changes, which may cause display unevenness.

  In FIGS. 8 to 10, the liquid crystal element using the ferroelectric liquid crystal is described as an example. However, the liquid crystal element using the anti-dielectric liquid crystal has the same problem.

  In this way, in the case of a memory-type liquid crystal element using smectic liquid crystal, no voltage is applied during the display screen holding period after display writing, so that when display unevenness occurs, it remains as it is and the next writing is performed. There is a problem that the image cannot be erased until it is removed, and a uniform display cannot be obtained.

  It is an object of the present invention to provide a liquid crystal element that can solve the above-described problems.

  Another object of the present invention is to provide a liquid crystal element using a smectic liquid crystal and capable of uniform display.

  The liquid crystal element according to the present invention includes a pair of substrates, a smectic liquid crystal sandwiched between the pair of substrates, an injection hole for injecting the smectic liquid crystal between the pair of substrates, and injection of the smectic liquid crystal between the pair of substrates. A plurality of scanning electrodes arranged perpendicular to the direction, a plurality of signal electrodes arranged perpendicular to the plurality of scanning electrodes, a plurality of scanning electrodes and an alignment film disposed on the plurality of signal electrodes; Further, the present invention is characterized by having voltage applying means for performing a scanning order for applying voltages to the plurality of scanning electrodes in order from the injection hole side toward the back side.

  The liquid crystal element according to the present invention includes a signal electrode between a pair of substrates and a scanning electrode arranged in a strip shape, an alignment film on the scanning electrode and the signal electrode, and a ferroelectric property between the pair of substrates. In a liquid crystal element having a liquid crystal layer sandwiched between liquid crystals, the scanning electrodes arranged in the strip shape are arranged perpendicular to the injection direction of the ferroelectric liquid crystal, and the order of scanning the voltage application to the scanning electrodes is It is characterized by being performed in order from the hole side to the back side.

  Furthermore, in the liquid crystal element according to the present invention, the alignment film is preferably a SiOx film formed by oblique deposition.

  Furthermore, in the liquid crystal element according to the present invention, the voltage application unit may stop voltage application to the plurality of scan electrodes after scanning all the plurality of scan electrodes from the injection hole side to the back side once. preferable.

  Furthermore, in the liquid crystal element according to the present invention, the smectic liquid crystal is preferably a ferroelectric liquid crystal or an anti-dielectric liquid crystal.

  Furthermore, the liquid crystal element according to the present invention preferably has a plurality of signal electrodes arranged perpendicular to the plurality of scanning electrodes.

  According to the liquid crystal element according to the present invention, the scanning electrode in the region where the alignment is likely to be unstable is scanned in the last order, so the non-selection pulse is applied after the selection pulse is applied. It has become possible to reduce the number of times. For this reason, it is possible to prevent the occurrence of display unevenness due to a change in white or black display caused by twist alignment. Therefore, display unevenness can be eliminated even in a region far from the injection hole of the liquid crystal element, and uniform display can be obtained.

  In the liquid crystal device according to the present invention, in particular, a pair of substrates each include a scanning electrode and a signal electrode, an SiOx alignment film formed by oblique vapor deposition is provided on the electrodes, and a liquid crystal layer made of ferroelectric liquid crystal is sandwiched between the substrates. In the liquid crystal element thus formed, display unevenness can be eliminated and uniform display can be obtained.

  The liquid crystal element according to the present invention will be described below with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and equivalents thereof.

  FIG. 11 is a diagram showing an outline of the liquid crystal panel 100 used in the present invention, and FIG. 12 is a cross-sectional view taken along the line AA ′ of FIG.

  The ferroelectric liquid crystal 108 is sandwiched between the two transparent glass substrates 101 a and 101 b and the sealant 102. A plurality of scanning electrodes 104 are arranged in a strip shape on the transparent glass substrate 101a. The plurality of scan electrodes 104 are arranged in a direction perpendicular to the direction in which the liquid crystal 108 is injected from the injection hole 103. A plurality of signal electrodes 105 are arranged in a band shape on the transparent glass substrate 101b. As described above, the region 106 far from the injection hole 103 is a region in which the alignment of the liquid crystal 108 tends to be unstable.

  The ferroelectric liquid crystal 108 behaves as described in FIGS. 1 and 2 described above. Moreover, the polarizing plates 15a and 15b shown in FIG. 1 are disposed outside the transparent glass substrates 101a and 101b, respectively.

  In the liquid crystal panel 100, predetermined scanning electrodes 104 and signal electrodes 015 are formed on a glass substrate 101 by transparent electrodes, respectively, and SiO alignment films 107a and 107b are formed by oblique deposition as SiOx films on the respective electrodes. . The pair of glass substrates 101 is held at a thickness of 1 to 2 μm by a spacer (not shown) and bonded by a sealant 102. The assembled empty cell is placed in a vacuum, and the ferroelectric liquid crystal 108 heated and melted is placed in the injection hole 103 to inject the ferroelectric liquid crystal 108 into the cell.

  FIG. 13 is a diagram showing a schematic configuration of the liquid crystal element 120.

  The liquid crystal element 120 applies a voltage waveform to the liquid crystal panel 100, the control unit 110, a drive voltage waveform control circuit 111, a scan drive voltage waveform generation circuit 112 for applying a voltage waveform to each scan electrode 104, and each signal electrode 105. Signal drive voltage waveform generation circuit 113, display data storage unit 114, RAM 115, ROM 116, and the like.

  The control unit 110 outputs a control signal to the drive voltage waveform control circuit 111 so that the display data stored in the display data storage unit 114 is displayed on the liquid crystal panel 100 in accordance with a program stored in the RAM 115 or the ROM 116 in advance. Is configured to do. Further, the drive voltage waveform control circuit 111 is configured to output a predetermined voltage waveform to the plurality of scan electrodes 104 and the plurality of signal electrodes 105 in accordance with the input control signal. The signal drive voltage waveform generation circuit 113 is controlled.

  As described above, the scanning electrode 104 is arranged perpendicular to the injection direction of the liquid crystal 108. Further, the voltage application order to the scan electrode 104 proceeds in order from the first to the final one from the injection hole 103 side to the back side in the same order as the injection direction of the liquid crystal 108 as shown by the arrows. The drive pulses applied to the scan electrode 104 and the signal electrode 105 have the same waveforms as those in FIGS. 6 (a) and 6 (b). The drive waveform applied to each pixel is the same as in FIG. As described above, since the scan electrodes 104 from the first to the last are scanned from the injection hole 103 side to the back side in the same order as the injection direction, the scan electrode 104 in the region 106 in which the orientation is likely to be unstable is obtained. The scanning order is last, and the number of times the non-selection pulse is applied after the selection pulse is applied is reduced. Therefore, even in the region 106 in which the orientation is likely to be unstable, the transition to the twist orientation is not performed, and display unevenness does not occur.

  Although the scanning electrode 104 of the liquid crystal panel 100 has a strip shape, even if it is a pixel shape electrode, the same effect can be obtained if it is arranged in a strip shape in the vertical direction. Further, in the liquid crystal panel 100, the SiO alignment film is used as the alignment film 107, but an SiO 2 film or the like can also be used.

  In a display element having a memory property, it is only necessary to scan once in the writing period in order to keep the display once written without erasing. In the region 106 where the alignment is unstable, the selection pulse is applied toward the end of the applied drive pulse, so that the number of times the non-selection pulse is repeated is reduced, and there is no uniform display without shifting to the twist alignment. Display is obtained. In particular, according to the method of the present invention, as the screen size increases, the density unevenness of the liquid crystal material also increases, and when the number of scan electrodes increases, the number of times the non-selection pulse is applied also increases. It is effective to obtain.

  In the liquid crystal element 120 described above, a ferroelectric liquid crystal is used. However, the anti-dielectric liquid crystal shown in FIGS. 3 and 4 can also be used for the liquid crystal element.

It is a figure which shows the structural example of the liquid crystal panel using a ferroelectric liquid crystal. It is a figure which shows the relationship between the applied voltage and light transmittance of a ferroelectric liquid crystal. It is a figure which shows the structural example of the liquid crystal panel using an anti-dielectric liquid crystal. It is a figure which shows the relationship between the applied voltage and light transmittance of an anti-dielectric liquid crystal. It is a figure which shows the area | region where alignment in the liquid crystal panel of a ferroelectric liquid crystal tends to become unstable. It is a figure which shows an example of the pulse applied to a scanning electrode. It is a figure which shows an example of the pulse applied to a signal electrode. It is a figure which shows an example of the drive pulse applied to a pixel. It is a figure which shows an example of the scanning method. It is a figure which shows the other example of the scanning method. It is a figure which shows the other example of the scanning method. It is a schematic block diagram of the liquid crystal panel used for this invention. It is sectional drawing in FIG. It is a schematic block diagram of the liquid crystal element which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Liquid crystal panel 101 Glass substrate 102 Sealant 103 Injection hole 104 Scan electrode 105 Signal electrode 106 Area | region where alignment is easy to become unstable 107 Orientation film | membrane 108 Liquid crystal layer 112 Scanning drive voltage waveform generation circuit 113 Signal drive voltage waveform generation circuit 120 Liquid crystal element

Claims (5)

A pair of substrates;
A smectic liquid crystal sandwiched between the pair of substrates;
An injection hole for injecting the smectic liquid crystal between a pair of substrates;
A plurality of scan electrodes disposed between the pair of substrates perpendicular to the injection direction of the smectic liquid crystal;
An alignment layer disposed on the plurality of scan electrodes;
A voltage applying means for performing a scanning order of applying a voltage to the plurality of scanning electrodes from the injection hole side toward the back side;
A liquid crystal element comprising:   The liquid crystal element according to claim 1, wherein the alignment film is a SiOx film formed by oblique deposition.   2. The liquid crystal element according to claim 1, wherein the voltage applying unit stops voltage application to the plurality of scan electrodes after scanning all the plurality of scan electrodes once from the injection hole side to the back side.   The liquid crystal element according to claim 1, wherein the smectic liquid crystal is a ferroelectric liquid crystal or an anti-dielectric liquid crystal.   5. The liquid crystal element according to claim 1, further comprising a plurality of signal electrodes arranged perpendicular to the plurality of scanning electrodes.

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